Use of peptides for imparting kokumi

ABSTRACT

The inventors of this invention have conducted the search for a variety of compounds which may possess a desired CaSR agonist activity to thus find out a substance capable of imparting a kokumi, which shows a more excellent kokumi-imparting effect, in particular, a kokumi-imparting effect of the initial taste-imparting type one, which is excellent in the stability and which can easily be produced at a low cost and the present invention thus provide a kokumi-imparting agent consisting of such a substance as well as a complex kokumi-imparting agent comprising the substance and other substances possessing the CaSR agonist activities in combination. More particularly, the present invention herein provides a kokumi-imparting agent consisting of γ-Glu-Abu (L-γ-glutamyl-L-2-amino-butyric acid) and a complex kokumi-imparting agent comprising the foregoing substance and another substance having a CaSR agonist activity, in combination.

This application is a Continuation of, and claims priority under 35 U.S.C. §120 to PCT/JP2010/055856, filed Mar. 31, 2010, and claims priority therethrough under 35 U.S.C. §119 to Japanese Application No. 2009-089347, filed Apr. 1, 2009, and Japanese Application No. 2009-291151, filed Dec. 22, 2009, the entireties of which are incorporated by reference herein. Also, the entirety of the Sequence Listing filed electronically herewith is hereby incorporated by reference herein (File name: 2011-09-30T_US-469_Seq_List; File size: 27 KB; Date recorded: Sep. 30, 2011).

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a kokumi-imparting agent and a complex kokumi-imparting agent, which consist of a peptide showing a CaSR agonist activity. Moreover, the present invention also relates to a seasoning composition which comprises a peptide showing a CaSR agonist activity in a concentration of not less than a predetermined level.

2. Brief Description of the Related Art

The consumers' demands on the taste and palatability of foods have recently been increased due to, for instance, the diversity of the human eating habits. In this connection, the taste and palatability of a food have conventionally been expressed by the five basic tastes, in other words, a sweet taste, a salty taste, a sour taste, a bitter taste and umami (deliciousness), but there has correspondingly been increased the needs for the development of an excellent kokumi-imparting agent capable of imparting, to a food, a “kokumi” which can impart, to a food, further improved tastes intensified even in, for instance, the thickness, the growth (or mouthfulness), the continuity and the harmony as the marginal tastes of the foregoing five basic tastes, which cannot be expressed only by these five basic tastes. On the other hand, the calcium sensing receptor (CaSR) is also referred as the calcium receptor, the signals outputted from the receptor can control a variety of biological functions within the living bodies and the substances possessing such a CaSR agonist activity can be used as a kokumi-imparting agent (International Patent Laid-Open No. 2007/055393, Pamphlet, International Patent Laid-Open No. 2008/139945, and Journal of Biological Chemistry, (2010), 285 (2), 1016-22as will be specified below).

There would be a variety of taste-developing patterns in the foregoing “kokumi”. In this respect, there has been an intensive need, in particular, for the development of a kokumi-imparting agent capable of imparting the kokumi, to a food, and having such a taste-developing pattern that it can develop or present the kokumi of the initial taste type one. Moreover, the substance for imparting the kokumi would in general be used in, for instance, foods and accordingly, it should be excellent in its stability. In addition, the substance for imparting the kokumi should be able to be easily produced at a low cost from the industrial standpoint.

Accordingly, there have been desired for the search for a variety of compounds possessing the desired CaSR agonist activity to thus find out a substance capable of imparting a kokumi to other substance (foods or drinks), which shows a more excellent kokumi-imparting effect, in particular, a kokumi-imparting effect of the initial taste-imparting type one, which is excellent in the stability and which can easily be produced at a low cost and to thereby provide a kokumi-imparting agent consisting of such a substance as well as a complex kokumi-imparting agent comprising the substance and other substances possessing the CaSR agonist activities in combination.

On the other hand, regarding some γ-glutamyl peptides each carrying a γ -glutamine residue at the N-terminal thereof, there have been known those synthesized as substrates, for instance, in the studies of the enzymatic activities (see International Patent Laid-Open No. 2007/066430, Pamphlet and Molecular Pharmacology (1982), 21(3), 629-36, Agricultural and Biological Chemistry (1981), 45(12), 2839-45, and Journal of Biological Chemistry (1979), 254(12), 5184-90, specified later), but there have not yet been known any case in which γ-Glu-Abu is used as a kokumi-imparting agent or a seasoning or further as an ingredient of a food. In this respect, the whole contents of International Patent Laid-Open No. 2007/055393, Pamphlet, International Patent Laid-Open No. 2007/066430, Pamphlet, and International Patent Laid-Open No. 2008/139945, Pamphlet are incorporated herein as references as if they were, in fact, expressly disclosed in this specification.

SUMMARY OF THE INVENTION Problems that the Invention is to Solve

It is an object of the present invention to search for a variety of compounds possessing the desired CaSR agonist activity to thus find out a substance capable of imparting a kokumi, which shows a more excellent kokumi-imparting effect, in particular, a kokumi-imparting effect of the initial taste-imparting type one, which is excellent in the stability and which can easily be produced at a low cost and to thereby provide a kokumi-imparting agent consisting of such a substance as well as a complex kokumi-imparting agent comprising the substance and other substances possessing the CaSR agonist activities in combination. It is a further object of the present invention to provide a seasoning composition which comprises the foregoing substance in a concentration of not less than the predetermined level.

Means for the Solution of the Problems

As a result of searching for a variety of compounds, the inventors of this invention have surprisingly found out that γ-Glu-Abu (L-γ-glutamyl-L-2-aminolactic acid) possesses a high CaSR agonist activity and a quite excellent kokumi-imparting effect and, in particular, the taste-developing pattern thereof would permit the impartment of a kokumi of the initial taste-imparting type to a subject. Furthermore, the inventors have found that γ-Glu-Abu thus discovered is excellent in the stability and has such a favorable taste-developing pattern that it has a stronger initial taste-imparting ability, as compared with those observed for γ-Glu-Cys as a dipeptide similar to the former. Moreover, γ-Glu-Abu thus discovered can serve, by itself, as a useful kokumi-imparting agent and a complex kokumi-imparting agent by combining the substance with other substances each showing a CaSR agonist activity and have thus completed the present invention.

More specifically, the present invention herein provides a kokumi-imparting agent consisting of γ-Glu-Abu. According to the present invention, there is further provided a complex kokumi-imparting agent which comprises, in combination, (a) γ-Glu-Abu and (b) one or at least two amino acids or peptides selected from the group consisting of γ-Glu-X-Gly wherein X represents an amino acid or an amino acid derivative, γ-Glu-Val-Y wherein Y represents an amino acid or an amino acid derivative, γ-Glu-Ala, γ-Glu-Gly, γ-Glu-Cys, γ-Glu-Met, γ-Glu-Thr, γ-Glu-Val, γ-Glu-Orn, Asp-Gly, Cys-Gly, Cys-Met, Glu-Cys, Gly-Cys, Leu-Asp, D-Cys, γ-Glu-Met (O), γ-Glu-γ-Glu-Val, γ-Glu-Val-NH₂, γ-Glu-Val-ol, γ-Glu-Ser, γ-Glu-Tau, γ-Glu-Cys (S—Me) (O), γ-Glu-Leu, γ-Glu-Ile, γ-Glu-t-Leu and γ-Glu-Cys (S—Me).

According to the present invention there is also provided a complex kokumi-imparting agent which comprises, in combination, (a) γ-Glu-Abu and (b) one or at least two peptides selected from the group consisting of those represented by the following general formula: γ-Glu-X—OCH—(Z)—CO₂H (wherein X represents an amino acid or an amino acid derivative and Z represents H (a hydrogen atom) or a CH₃ group (a methyl group)); and those represented by the foregoing general formula: γ-Glu-Val-Y (wherein Y represents GlyA or LacA).

Further, the present invention herein provides a seasoning composition (hereunder also referred to as “seasoning composition of the present invention”) which comprises γ-Glu-Abu in an amount of not less than 1,000 ppm by mass, preferably not less than 2,000 ppm by mass and more preferably not less than 2,500 ppm by mass.

According to a further aspect of the present invention, there is also provided a method for the preparation of a food and a drink comprising the steps of adding an ingredient for a food or a drink, which contains γ-Glu-Abu in an amount of not less than 1,000 ppm by mass, preferably not less than 2,000 ppm by mass and more preferably not less than 2,500 ppm by mass to an ingredient for other foods and drinks and optionally treating or cooking the resulting mixture of these ingredients. The present invention also provided the food or the drink or an intermediate product used for the production of a food or a drink, prepared according to the preparation method.

In addition, the present invention further provides a food or a drink or an intermediate product for the preparation of a food or a drink, which comprises γ-Glu-Abu in an amount ranging from 20 to 200 ppm by mass; at least one organic acid or salt thereof selected from the group consisting of lactic acid, citric acid, malic acid and succinic acid and salts thereof in an amount ranging from 0.005 to 0.1% by mass; and common salt in an amount ranging from 0.01 to 0.5% by mass; as well as a carrier acceptable for foods and drinks, and/or one or at least two of ingredients for seasoning.

According to a further aspect of the present invention, there is also provided a method for enhancing the flavor and/or the taste of a food or a drink, which comprises the step of incorporating, into a food or a drink, a composition containing γ-Glu-Abu in an amount of not less than 400 ppm by mass, preferably not less than 1,000 ppm by mass, more preferably not less than 2,000 ppm by mass and further preferably not less than 2,500 ppm by mass.

Effects of the Invention

The present invention would be able to provide a kokumi-imparting agent which is quite excellent in its kokumi-imparting effect and, in particular, has an excellent and unique kokumi-imparting effect of the initial taste-imparting type one represented by, for instance, such a taste-developing pattern that it shows a profile as shown in, for instance, the single figure, which is also excellent in the stability and which can easily be prepared at a low cost, as well as a complex kokumi-imparting agent containing the same. In addition, the present invention can likewise provide an excellent seasoning composition which comprises a substance possessing an excellent kokumi-imparting effect in a concentration of not less than a predetermined level.

The kokumi-imparting agent according to the present invention shows the flavor and/or taste-developing pattern quite similar to that observed for common salt and therefore, when using the kokumi-imparting agent, the latter can impart, to a low salt food or the like, a salty taste-like thick impression and an initial taste-punch (or impact) to the low salt food. Accordingly, the resulting food containing the agent of the present invention can maintain its salty taste impression like that prior to the reduction of the salt content even when the salt content of the food is reduced and therefore, the agent according to the present invention permits the production of a food highly beneficial to health. Examples of such foods include a variety of soups and various kinds of sauces. Especially, if eating a food containing the kokumi-imparting agent according to the present invention, the consumer can feel the salty taste-like thick impression and an initial taste-punch (or impact) immediately after eating the same.

BRIEF DESCRIPTION OF THE DRAWING

The single drawing FIGURE shows the taste and palatability profile (taste-developing pattern) observed for a kokumi-imparting agent of the initial taste type one.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The kokumi-imparting agent of the present invention consists of γ-Glu-Abu and it is sufficient that the agent essentially consists of γ-Glu-Abu from the viewpoint of the taste and accordingly, the agent may further comprise other components to such an extent that they do not exert any substantial influence on the agent of the invention in respect of the taste thereof.

The kokumi-imparting agent of the present invention or γ-Glu-Abu can also be used in combination with at least one additional ingredient for seasonings selected from the group consisting of amino acids such as sodium glutamate (MSG), nucleic acids such as inosine monophosphate (IMP), inorganic salts such as sodium chloride, organic acids such as citric acid, and various kinds of yeast extracts to thus provide a favorable seasoning composition which is improved in its kokumi, as compared with those obtained by the use of such additional ingredients for seasonings individually. When using γ-Glu-Abu in combination with the foregoing additional ingredients for seasonings, the concentration of the latter can easily or properly be determined or established by one of ordinary skill in the art after conducting investigations through, for instance, the sensory test.

The seasoning composition of the present invention or one containing not less than 1,000 ppm by mass of γ-Glu-Abu can likewise be combined with other ingredients for seasonings to thus provide more favorable separate seasonings.

In the present invention, the term “kokumi” means the taste which cannot be expressed by the five basic tastes or the sweet taste, the salty taste, the sour taste, the bitter taste and the umami and more specifically means the taste in which the marginal tastes of the basic ones such as the thickness, the growth (mouthfulness), the continuity and the harmony are enhanced in addition to the basic tastes. In addition, the term “kokumi-impartment” herein used means that the five basic tastes expressed by the sweet taste, the salty taste, the sour taste, the bitter taste and the umami are enhanced, while the marginal tastes of the basic tastes such as the thickness, the growth (mouthfulness), the continuity and the harmony associated with the former are simultaneously imparted to a subject. Moreover, this can also be referred to as the flavor-enhancing action. Therefore, γ-Glu-Abu serving as the kokumi-imparting agent of the present invention can likewise be referred to as a “flavor enhancer”. The kokumi-imparting agent according to the present invention or γ-Glu-Abu may also be used as a sweet taste enhancer, a salty taste enhancer, a sour taste enhancer, a bitter taste enhancer or an umami enhancer. Moreover, the taste of a food may vary with the elapse of time after eating the same and the taste of a food after eating the same is in general referred to as the initial taste, the middle taste and the after taste, in order, immediately after eating the food. Although they are indeed the relative concept, but the initial taste, the middle taste and the after taste of a subject are, as a whole, defined to be the taste observed within the term extending from 0 to 2 seconds, 2 to 5 seconds and not less than 5 seconds after eating the same, respectively. The taste observed during the term extending from 0 to 5 seconds is herein referred to as the “initial/middle taste” and that observed during the term extending from 2 to about 30 seconds is referred to as the “middle/after taste” (see the data plotted on the single FIGURE). Regarding the evaluation of the taste in case where the taste is divided into three subdivisions, it is difficult for the panelists (persons who eat the food to be examined) to concentrate their attention on the evaluation and the habitually used test comprises the evaluation of the taste while dividing it into two subdivisions.

The effects of a substance showing a CaSR activity on the kokumi and the taste-developing pattern can be confirmed by a method, for instance, a human sensory test for the evaluation of taste. An example of such a human sensory test for the evaluation of taste is one illustrated in Examples of this patent application, but the sensory test for the evaluation of taste usable herein is not restricted to this specific one.

The term “CaSR” used in this specification means the calcium sensing receptor which belongs to the class C of the 7-time transmembrane receptor and which is thus also referred to as “calcium receptor”. The term “CaSR agonist” used in this specification means a substance which is linked with the foregoing CaSR to thus activate the receptor. In addition, the term “activate CaSR” used herein means that a ligand is linked with CaSR to thus activate a protein linked with guanine nucleotide and to transmit signals outputted from the same. Moreover, the ability of a substance to form a linkage with CaSR to thus activate the same is referred to as “CaSR agonist activity”.

Now, a method for screening a compound having a CaSR agonist activity will specifically be presented hereunder, but the steps for screening the compound are not limited to those specified below at all.

-   -   1) A step for adding a test substance to a CaSR         activity-measuring system used for determining the CaSR activity         and a step for the determination of the CaSR activity;     -   2) A step for comparing the CaSR activity observed when adding         the test substance to the activity-measuring system with that         observed prior to the addition of the substance; and     -   3) A step for selecting a substance which shows the CaSR agonist         activity when it is added to the CaSR activity-measuring system.

The determination of the CaSR activity can likewise be carried out while using, for instance, a measuring system which makes use of cells having an ability of expressing CaSR. The foregoing cells may be those endogeneously expressing CaSR or genetically recombinant cells into which a CaSR-expression gene is exogeneously introduced. The aforementioned CaSR activity-measuring system is not restricted to any specific one inasmuch as it permits the detection of the linkage (or a reaction) between the CaSR-activation substance and CaSR, or it can emit or output a detectable signal in response to the formation of the linkage (or a reaction) between the CaSR-activation substance and CaSR within the cells, when adding an extracellular ligand (activating substance) specific to CaSR to the foregoing cells having an ability of expressing CaSR. If the CaSR activity is detected through the reaction with a test substance, it would be judged that the test substance shows the desired CaSR-stimulation activity.

An example of the foregoing CaSR preferably used herein is human CaSR encoded by the human CaSR gene registered under the GenBank Accession Number of NM_(—)000388. In this respect, however, the CaSR is not restricted to the protein encoded by the gene having the foregoing sequence of the registered CaSR and it may be any protein capable of being encoded by a gene having not less than 60%, preferably not less than 80% and more preferably not less than 90% of the sequence homology with the foregoing gene sequence, inasmuch as the protein encoded by such a gene possesses the CaSR function. In this connection, the CaSR function can be examined by making cells express these genes and then determining any change of an electric current and/or any change in the calcium ion concentration within the cells observed when calcium is added to the system containing the cells.

Regarding the foregoing CaSR, the source thereof is not restricted to any particular one and it may be those derived from the whole kinds of animals including mice, rats and canines, in addition to the foregoing human CaSR.

As has been discussed above, the CaSR activity can be confirmed through the use of the living cells capable of expressing CaSR or a fragment thereof, the cell membranes which can express CaSR or a fragment thereof, or an in vitro system including CaSR or a protein as a fragment thereof.

An example which makes use of living cells will be given below, but the present invention is by no means limited to this example at all.

CaSR is expressed in cultured cells such as oocytes of xenopus, ovarian cells derived from hamsters, and human fetal renal cells. This expression of CaSR can be carried out by introducing, into a plasmid possessing an exogenous gene, the CaSR gene which has been subjected to the cloning treatment in the form of a plasmid or cRNA obtained using the same as a template. Usable for the detection of such a reaction may be an electrophysiological means or a fluorescent indicator for the detection of any increase of the calcium concentration within the cells.

The expression of CaSR is initially confirmed by the presence of any response observed when adding calcium or an activator having the specificity thereto. More specifically, usable herein as the desired cells are those in which an intracellular electric current is detected when adding calcium in a concentration of about 5 mM or those in which the emission of fluorescent rays are observed upon the addition of a fluorescent indicator. In this connection, the concentration of calcium added to the cells is variously changed to determine any calcium concentration-dependency of the intensity of the intracellular electric current. Then a test substance is diluted to a concentration ranging from about 1 μM to 1 mM, the resulting dispersion is added to oocytes or cultivated cells and subsequently the CaSR activity in the presence of the foregoing test substance is measured to thus determine the CaSR agonist activity of the test substance.

More specifically, usable herein as such a test for the determination of the CaSR agonist activity is, for instance, the test illustrated in Test Examples disclosed in this specification, but the activity-determining test is not limited to such a specific one at all.

The amino acids or peptides used in the kokumi-imparting agent according to the present invention in combination with γ-Glu-Abu include, for instance, one or at least two amino acids or peptides selected from the group consisting of γ-Glu-Abu and γ-Glu-X-Gly (wherein X represents an amino acid or an amino acid derivative), γ-Glu-Val-Y (wherein Y represents an amino acid or an amino acid derivative), γ-Glu-Ala, γ-Glu-Gly, γ-Glu-Cys, γ-Glu-Met, γ-Glu-Thr, γ-Glu-Val, γ-Glu-Orn, Asp-Gly, Cys-Gly, Cys-Met, Glu-Cys, Gly-Cys, Leu-Asp, D-Cys, γ-Glu-Met (O), γ-Glu-γ-Glu-Val, γ-Glu-Val-NH₂, γ-Glu-Val-ol, γ-Glu-Ser, γ-Glu-Tau, γ-Glu-Cys (S—Me) (O), γ-Glu-Leu, γ-Glu-Ile, γ-Glu-t-Leu and γ-Glu-Cys (S—Me). In this respect, the amino acids may likewise include, for instance, neutral amino acids such as Gly, Ala, Val, Leu, Ile, Ser, Thr, Cys, Met, Asn, Gln, Pro, Hyp, t-Leu; acidic amino acids such as Asp, Glu; basic amino acids such as Lys, Arg, His; aromatic amino acids such as Phe, Tyr, Trp; as well as homoserine, citrulline, ornithine, α-aminobutyric acid, norvaline, norleucine, and taurine. Moreover, the amino acids used herein may also be artificial amino acids (having non-proteinaceous construction) such as tert-leucine, cyclo-leucine, α-aminoiso-butyric acid, L-penicillamine, allothreonine, and allo-isoleucine. In this connection, in the peptide: γ-Glu-X-Gly, X may be the aforementioned amino acid or derivative thereof, but preferably used herein are amino acids or derivatives thereof other than Cys.

In addition, the amino acids or peptides used in combination with γ-Glu-Abu in the kokumi-imparting agent of the present invention may be peptide derivatives each having a structure represented by the formula: γ-Glu-X—OCH—(Z)CO₂H, wherein X represents an amino acid or an amino acid derivative and Z represents H (hydrogen atom) or CH3 (methyl group). Moreover, the amino acids or peptides used herein may likewise be the compounds represented by the foregoing general formula: γ-Glu-Val-Y in which Y represents GlyA or LacA. Specific examples thereof preferably used herein are γ-Glu-Val-GlyA, γ-Glu-tLeu-GlyA, γ-Glu-Abu-GlyA, γ-Glu-Val-LacA, γ-Glu-tLeu-LacA and γ-Glu-Abu-LacA. In this respect, the term “GlyA” herein used means glycolic acid and LacA means butyric acid. Butyric acid may be either its S-isomer or its R-isomer, but it is preferably the S-isomer thereof. The following are the structural formulas of these compounds

In particular, the kokumi-imparting agent according to the present invention consists of γ-Glu-Abu and this agent has a unique and excellent initial taste type kokumi-imparting effect and the taste-developing profile as shown in the single figure. Accordingly, it is preferred that γ-Glu-Abu is used in combination with a peptide such as γ-Glu-Val-Gly, which shows a taste-developing profile different from that of the former.

In the specification of this patent application, each amino acid (residue) is expressed in terms of the following abbreviated form:

-   -   (1) Gly: glycine;     -   (2) Ala: alanine;     -   (3) Val: valine;     -   (4) Leu: leucine;     -   (5) Ile: isoleucine;     -   (6) Met: methionine;     -   (7) Phe: phenylalanine;     -   (8) Tyr: tyrosine;     -   (9) Trp: tryptophans;     -   (10) His: histidine;     -   (11) Lys: lysine;     -   (12) Arg: arginine;     -   (13) Ser: serine;     -   (14) Thr: threonine;     -   (15) Asp: aspartic acid;     -   (16) Glu: glutamic acid;     -   (17) Asn: asparagine;     -   (18) Gln: glutamine;     -   (19) Cys: cysteine;     -   (20) Pro: proline;     -   (21) Orn: ornithine;     -   (22) Sar: sarcosine;     -   (23) Cit: citrulline;     -   (24) N-Val: (or Nva): norvaline (2-aminovaleric acid);     -   (25) N-Leu (or Nle): norleucine;     -   (26) Abu: α-aminobutyric acid;     -   (27) Tau: taurine;     -   (28) Hyp: hydroxy-proline;     -   (29) t-Leu: tert-leucine;     -   (30) Cle: cyclo-leucine;     -   (31) Aib: α-amino-isobutyric acid (2-methyl-alanine);     -   (32) Pen: L-penicillamine;     -   (33) allo-Thr: allothreonine;     -   (34) allo-Ile: allo-isoleucine.

Furthermore, the term “amino acid derivative” used herein means a variety of derivatives of the foregoing amino acids and specific examples thereof include special amino acids and artificial amino acids, amino alcohols, or amino acids whose side chains such as terminal carboxyl groups, amino groups and/or thiol group of cysteine are substituted with a variety of substituents. Examples of such substituents include an alkyl group, an acyl group, a hydroxyl group, an amino group, an alkylamino group, a nitro group, a sulfonyl group or a variety of protective groups. Thus, examples of such amino acid derivatives include Arg (NO₂): N-γ-nitro-alginine, Cys (SNO): S-nitro-cysteine, Cys (S—Me): S-methyl cysteine, Cys (S-allyl) S-allyl cysteine, Val-NH₂: valine-amide, and Val-ol: valinol (2-amino-3-methyl-1-butanol). In the meantime, the peptide: γ-Glu-Cys(SNO)-Gly used herein is one represented by the following structural formula and the symbol: “(O)” appearing in the foregoing formulas: γ-Glu-Met (O) and γ-Glu-Cys (S—Me) (O) means that these peptides each have a sulfoxide structure. The symbol “(γ)” of γ-Glu means that another amino acid is linked with the glutamic acid through the carboxyl group situating at the γ-position of the latter.

S-Nitrosoglutathione (GNSO)

The γ-Glu-Abu used in this specification means L-γ-glutamyl-L-2-aminobutyric acid. The γ-Glu-Abu and the amino acids and peptides used in combination in the present invention may be commercially available ones if they can be purchased on the market, or can be obtained according to any known technique such as (1) chemical synthetic methods or (2) a method which makes use of an enzyme reaction, but it would be more convenient to use a chemical synthetic technique. The γ-Glu-Abu used in the present invention is very short in its length since it includes only two amino acid residues and therefore, it is more convenient to adopt a chemical synthetic technique. More specifically, it can be produced simply and at a low cost as compared with any tripeptide comprising three amino acid residues and accordingly, the use of this dipeptide is quite advantageous from the industrial standpoint. In addition, when chemically synthesizing the γ-Glu-Abu used in the present invention and the amino acids and peptides used in combination therewith, the preparation thereof may be carried out by synthesizing or semi-synthesizing these oligo-peptides while using a peptide-synthesis device. As such a method for chemically synthesizing these peptides, usable herein may be, for instance, the solid-phase peptide-synthesis technique. The peptide thus produced can subsequently be purified according to the usual techniques such as the ion-exchange chromatography technique, the reversed phase high performance liquid chromatography technique, or the affinity chromatography technique. Such a solid phase peptide-synthesis technique and the subsequently used peptide-purification technique are well known in the field of this art.

Alternatively, when producing the γ-Glu-Abu used in the present invention and the amino acids and peptides used in combination therewith, while making use of an enzyme reaction, the preparation thereof may be carried out by the use of the method disclosed in the pamphlet of International Patent Laid-Open WO 2004/011653. More specifically, they can be prepared by reacting an amino acid or a peptide, in which one of the terminal carboxyl group thereof is esterified or aminated, with another amino acid whose amino group is in its free state (for instance, an amino acid whose carboxyl group is protected) in the presence of a peptide-forming enzyme and then purifying the resulting dipeptide or tripeptide. Examples of such peptide-forming enzymes are cultures of microorganisms showing the ability of producing a peptide; the cell bodies of microorganisms isolated from the culture; or a product obtained by processing the cell bodies of the microorganisms, or a peptide-forming enzyme originated from the microorganisms. In the meantime, it is herein construed that the disclosure of WO 2004/011653 is included in the description of this specification.

In addition to the foregoing enzymatic production methods and chemical synthesis methods, the peptides used in the present invention are often included in naturally occurring products, for instance, plants such as vegetables and fruits, microorganisms such as yeast and other natural resources. When they are present in naturally occurring substances, they can be isolated from the same and the resulting isolated products can likewise be used in the present invention.

The kokumi-imparting agent or the complex kokumi-imparting agent according to the present invention can be used as a seasoning without any particular post-treatment or can be mixed with carriers acceptable for foods and drinks or ingredients for other seasonings to thus give various seasonings. Examples of such other ingredients for seasonings include spices, saccharides, sweeteners, edible fibers, vitamins, amino acids such as sodium glutamate (MSG), nucleic acids such as inosine monophosphate (IMP), inorganic salts such as sodium chloride, and organic acids such as citric acid or salts thereof as well as various kinds of yeast extracts.

Incidentally, low salt foods preferred as food compositions each comprising the kokumi-imparting agent or the complex kokumi-imparting agent according to the present invention are, by nature, those containing common salt and, in particular, foods whose common salt content is reduced. The low salt foods include not only those in the solid form, but also those in the liquid form, and the term “low salt food” is synonymous with the “low salt food and drink”.

Examples of such low salt foods include dairy products such as butter and cheese; animal oils and fats-containing and/or vegetable oils and fats-containing foods such as margarine, sauces and roux; emulsified foods such as dressings and mayonnaise; various kinds of curry and stew; various kinds of snack foods; and a variety of soups containing meat extracts or essences of meat and/or cream. Moreover, such low salt foods likewise include, for instance, fermented or brewed foods such as miso and soy sauce; soups or broths and sauces which make use of such fermented or brewed foods; processed vegetable foods such as salted vegetables and pickles; meat-processed products such as hams and sausage; processed marine products such as boiled fish paste, dried marine products and foods boiled down in soy; cooked meat balls, hamburger steak; fried foods; and grilled chicken. Among these, preferred low salt foods are those having a common salt concentration, upon eating the same, ranging from 0.01 to 0.5% by mass. Moreover, it is also preferred to use at least one member selected from the group consisting of organic acid such as lactic acid, citric acid, malic acid and succinic acid, and salts thereof in combination with common salt, in an amount ranging from 0.005 to 0.1% by mass. The use of these ingredients in combination would permit the further improvement of the salty taste-enhancing effect of the kokumi-imparting agent or γ-Glu-Abu of the present invention.

According to the present invention, there is also provided a food or drink comprising 20 to 200 ppm by mass of γ-Glu-Abu and 0.01 to 0.5% by mass of common salt. In this respect, it is preferred that the food or drink further comprises at least one member selected from the group consisting of organic acid such as lactic acid, citric acid, malic acid and succinic acid, and salts thereof in a concentration ranging from 0.005 to 0.1% by mass.

If the kokumi-imparting agent of the present invention is incorporated into the foregoing low salt foods, the foods would be able to give, to the consumer, a salty taste-like thick impression and an initial taste-punch (or impact) at the initial stage, when they eats these low salt foods.

The γ-Glu-Abu used in the present invention and the amino acids or peptides used in combination therewith may likewise include those in their salt form. If the γ-Glu-Abu used in the present invention and the amino acids or peptides used in combination therewith are present in their salt form, the salts are not restricted to specific ones insomuch as they are pharmacologically acceptable and specific examples thereof include ammonium salts, salts with alkali metals such as sodium and potassium, salts with alkaline earth metals such as calcium and magnesium, aluminum salts, zinc salts, salts with organic amines such as triethylamine, ethanolamine, morpholine, pyrrolidine, piperidine, piperazine and dicyclo-hexylamine, and salts with basic amino acids such as arginine and lysine, for the acidic groups such as carboxyl groups. Moreover, examples of the foregoing compounds likewise include salts with inorganic acids such as hydrochloric acid, sulfuric acid, phosphoric acid, nitric acid and hydrobromic acid; salts with organic acids such as acetic acid, citric acid, benzoic acid, maleic acid, fumaric acid, tartaric acid, succinic acid, tannic acid, butyric acid, hibenzoic acid, pamoic acid, enanthic acid, decanoic acid, theoclic acid, salicylic acid, lactic acid, oxalic acid, mandelic acid and malic acid; and salts with organic sulfonic acids such as methanesulfonic acid, benzenesulfonic acid and p-toluenesulfonic acid, for the basic groups of the compounds.

The kokumi-imparting agent or the complex kokumi-imparting agent according to the present invention can be used in any form such as dried powders, pastes, and solutions, without any restriction in the physical properties thereof.

The kokumi-imparting agent or the complex kokumi-imparting agent according to the present invention can be used for incorporating into, for instance, foods, drinks and seasonings.

If the kokumi-imparting agent or the complex kokumi-imparting agent according to the present invention is used for incorporating into, for instance, foods, drinks and seasonings, the ultimate amount of the γ-Glu-Abu and that of the amino acid or peptide used in combination therewith are not restricted to any specific one inasmuch as they can ensure the achievement of the desired effects of the present invention, but the amount of γ-Glu-Abu and/or that of the amino acid or peptide each fall within the range of from about 1 ppb by mass to 99.9% by mass and preferably about 10 ppb by mass to 10% by mass and more preferably about 1 ppm by mass to 1% by mass on the basis of the total mass of each corresponding food, drink, seasoning or the like.

According to a further aspect of the present invention, there is also provided a method for the preparation of a seasoning composition which comprises the step of mixing the kokumi-imparting agent of the present invention with a carrier acceptable for the ingredients for other seasonings or foods and drinks. The concentration of γ-Glu-Abu in the seasoning composition thus prepared particularly preferably ranges from 400 to 500,000 ppm by mass. In particular, the method for the preparation of a seasoning composition according to the present invention preferably comprises the steps of mixing the kokumi-imparting agent with the ingredients of another seasoning and controlling the concentration of γ-Glu-Abu in the seasoning composition thus prepared to a level ranging from 400 to 500,000 ppm by mass.

The present invention further provides a method for the preparation of a food or drink, which comprises the step of incorporating the kokumi-imparting agent of the present invention into an ingredient for other foods or drinks. The concentration of γ-Glu-Abu in the food or drink thus prepared particularly preferably ranges from 20 to 200 ppm by mass. Accordingly, it is herein preferred that the step for the incorporation of the kokumi-imparting agent of the present invention into a food or drink comprises the step of adjusting the concentration of γ-Glu-Abu in the food or drink thus prepared to a level ranging from 20 to 200 ppm by mass.

The food, drink, seasoning or the like, which comprises the incorporated kokumi-imparting agent or complex kokumi-imparting agent according to the present invention, may further comprise, for instance, any solid or liquid carrier and/or appropriate seasoning ingredients, which are acceptable for foods and drinks.

As the foregoing carriers, there can be listed, for instance, glucose, lactose, saccharose, starch, mannitol, dextrin, fatty acid glycerides, polyethylene glycol, hydroxyethyl starch, ethylene glycol, polyoxyethylene sorbitan fatty acid esters, gelatine, albumin, amino acids, water, and physiological saline.

The aforementioned ingredients for seasoning are not restricted to any particular one and they may be any ones currently used in this field, but specific examples thereof are those already described above.

The contents of the foregoing carriers, other seasoning ingredients or the like are not restricted to specific ones.

The seasoning composition of the present invention comprises γ-Glu-Abu in an amount of not less than 1,000 ppm by mass, preferably 2,000 ppm by mass and more preferably 2,500 ppm by mass. These seasonings particularly suitably show the taste-imparting effect of γ-Glu-Abu. The rate of γ-Glu-Abu occupying the seasoning composition of the present invention is preferably not less than 3,000 ppm by mass, more preferably 5,000 ppm by mass, further preferably not less than 1% by mass, particularly preferably not less than 3% by mass. Further, preferred also include those having a content of γ-Glu-Abu of not more than 99.9% by mass. The components of the seasoning composition according to the present invention other than γ-Glu-Abu are not restricted to specific ones and specific examples thereof include carriers and seasoning ingredients, which are acceptable for foods and drinks.

More specific examples of the seasonings of the present invention are yeast extracts each containing γ-Glu-Abu in an amount of not less than 2,500 ppm by mass. The yeast extract is not particularly restricted in any of the cell bodies of microorganisms, from which the extract is originated, the conditions of cultivating the microorganisms and the methods for the extraction thereof and accordingly, any yeast extract can be used in the seasoning composition of the present invention. Furthermore, these yeast extracts may be ones which have been subjected to, for instance, a heat-treatment, a treatment with an enzyme, a concentration treatment and/or a treatment for converting the same into powder. The method for the preparation of such a yeast extract containing not less than 2,500 ppm by mass of γ-Glu-Abu is not limited to any particular one, but such a yeast extract product may be obtained by, for instance, adding γ-Glu-Abu to a yeast extract in such a manner that the concentration of the former falls within the range specified above.

The seasoning composition of the present invention may be used in any form and may be in the form of, for instance, a dried powder, a paste and a solution, without any restriction in the physical properties thereof.

The seasoning composition of the present invention can be used for the incorporation thereof into, for instance, foods and drinks.

The present invention further provides a method for the preparation of another type of a seasoning composition, which comprises the step of adding the seasoning of the present invention to other seasoning ingredients or a carrier acceptable for foods and drinks. The concentration of γ-Glu-Abu in the seasoning composition prepared according to this method particularly preferably ranges from 400 to 500,000 ppm by mass. In particular, the method for the preparation of this type of a seasoning composition according to the present invention preferably comprises the steps of mixing the seasoning composition of the present invention with other seasoning ingredients and then controlling the concentration of γ-Glu-Abu in this type of a seasoning composition thus prepared to a level ranging from 400 to 500,000 ppm by mass.

The present invention further provides a method for the preparation of a food or drink, which comprises the step of incorporating the seasoning composition of the present invention into other ingredients used for preparing a food or drink. The concentration of γ-Glu-Abu in the food or drink thus prepared particularly preferably ranges from 20 to 200 ppm by mass. In particular, it is herein preferred that the step for the incorporation of the seasoning composition of the present invention into other ingredients used for preparing a food or drink comprises the step of adjusting the concentration of γ-Glu-Abu in the food or drink thus prepared to a level ranging from 20 to 200 ppm by mass.

According to the present invention, there is also provided a method for the preparation of, for instance, a food, a drink or a seasoning, which comprises the step of adding, to an intermediate used for the production of, for instance, a food, a drink or a seasoning, γ-Glu-Abu in such a manner that the resulting food, drink or seasoning contains γ-Glu-Abu in an amount ranging from 1 ppb by mass to 99.9% by mass. In this respect, the food, drink, seasoning or the like is preferably a low salt food.

The present invention also provides a method for the preparation of a food or a drink, which comprises the step of incorporating the seasoning composition of the present invention into an intermediate used for preparing such a food or drink. In this connection, the food or drink is preferably a low salt food.

In the method for preparing a food or drink, or an intermediate used for the preparation of a food or drink according to the present invention, it is also possible to use, for instance, the aforementioned yeast extract containing γ-Glu-Abu in a high concentration, as an ingredient used for preparing a food or drink, which comprises not less than 1,000 ppm by mass of γ-Glu-Abu and is used for the preparation of another food or drink. Moreover, usable herein as such ingredients likewise include, for instance, γ-Glu-Abu products prepared according to a chemical or enzymatic synthetic method and then isolated; or the diluted and/or dispersed product of the resulting γ-Glu-Abu products thus isolated. Examples of such diluted and/or dispersed products containing γ-Glu-Abu include those obtained by diluting the powdery product of γ-Glu-Abu with any solid or liquid carriers acceptable for foods and drinks, which have already been listed above.

In the present invention, the phrase “ingredients used for preparing other foods or drinks” is herein intended to include all kinds of ingredients for foods and drinks currently used as raw materials for foods and drinks except for the “ingredients for foods and drinks containing not less than 1,000 ppm by mass of γ-Glu-Abu” and specific examples thereof include those listed below as foods and drinks and intermediates for preparing them, in addition to the aforementioned carriers and ingredients for seasoning, which are acceptable for foods and drinks.

The method for preparing a food or a drink or an intermediate used for preparing the same according to the present invention may comprise the step for further processing or cooking the mixture of ingredients for foods and drinks, which is obtained through the step of incorporating an ingredient for foods and drinks containing not less than 1,000 ppm by mass of γ-Glu-Abu into other ingredients for foods and drinks. In this respect, the term “processing or cooking” herein used include any cooking step commonly used in this field.

Examples of such cooking steps include roasting, baking or broiling, boiling, frying, steaming, cutting, crushing or smashing, grating, rubbing and grating, mashing, grinding and mashing, mincing, blending, sieving and pounding steps, but the present invention is not restricted to these specific cooking steps.

Examples of the foods and drinks or the intermediates used for preparing them, which can be prepared according to the method of the present invention, include those already listed above, i.e., dairy products such as butter and cheese; animal oils and fats-containing and/or vegetable oils and fats-containing foods such as margarine, sauces and roux; emulsified foods such as dressings and mayonnaise; various kinds of curry and stew; various kinds of snack foods; and various kinds of soups containing meat extracts or essences of meat and/or cream. Moreover, such foods and drinks or intermediates used for preparing the same likewise include, for instance, fermented or brewed foods such as miso and soy sauce; soups or broths and sauces which make use of such fermented or brewed foods; processed vegetable foods such as salted vegetables and pickles; meat-processed products such as hams and sausage; processed marine products such as boiled fish paste, dried marine products and foods boiled down in soy; cooked meat balls and hamburger steak; fried foods; and grilled chicken.

The foods and drinks of the present invention also include foods or drinks as the completed products in such forms that they are currently put on the market and can be eaten and the term “intermediates used for preparing foods and drinks” is herein intended to mean all of those having any form prior to processing the same into the completed products. When using the intermediate used for preparing a food or a drink as a seasoning ingredient containing γ-Glu-Abu, it is preferred that the intermediate comprises γ-Glu-Abu in an amount ranging from about 400 to 500,000 ppm by mass, and preferably about 4,000 to 40,000 ppm by mass and such an intermediate can be prepared by adding an ingredient for foods and drinks containing, for instance, not less than 1,000 ppm by mass of y -Glu-Abu in such a manner that the resulting intermediate has a concentration thereof falling within the range specified above. Alternatively, the final or completed product preferably comprises about 20 to 200 ppm by mass of γ-Glu-Abu as expressed in terms of the concentration at the time of eating the same or that thereof in the food or drink as the final product and such a final product can be prepared by adding an ingredient for foods and drinks containing, for instance, not less than 1,000 ppm by mass of γ-Glu-Abu in such a manner that the resulting final product has a concentration thereof falling within the range specified above.

In the method for the preparation of a food or a drink or an intermediate used for preparing the same, according to the present invention, the step of adding, to an ingredient for preparing other foods or drinks, the ingredient used for preparing a food or a drink, which comprises γ-Glu-Abu, preferably comprises the step of controlling the concentration of γ-Glu-Abu in the resulting intermediate to a level of 400 to 500,000 ppm by mass and the method of the present invention more preferably comprises an additional step of adding the intermediate used for preparing foods or drinks to an ingredient used for preparing other foods and drinks to thus adjust the concentration of γ-Glu-Abu in the resulting food or drink to a level ranging from 20 to 200 ppm by mass.

In the method for preparing a food or a drink according to the present invention, the step for adding an ingredient used for preparing a food or a drink, which comprises γ-Glu-Abu, to an ingredient for preparing other foods or drinks preferably comprises the step of controlling the concentration of γ-Glu-Abu in the resulting food or drink to a level of 20 to 200 ppm by mass.

The method for preparing a food or a drink according to the present invention is suitable for the cases in which the food or drink is a low salt one. In this case, it is preferred that the method comprises an additional step of adding, to an ingredient for foods or drinks, at least one member selected from the group consisting of organic acids such as lactic acid, citric acid, malic acid and succinic acid, and salts thereof, and preferably lactic acid and malic acid in such a manner that the concentration thereof in the resulting food or drink falls within the range of from 0.005 to 0.1% by mass, and it is likewise preferred that the method further includes the step of adding common salt to the ingredient for foods or drink in an amount smaller than that observed when preparing the corresponding and existing food or drink. In this respect, the term “small amount of common salt in a low salt food” herein used means, for instance, the common salt concentration, in the low salt food, of at least 5% and preferably at least 10% smaller than that observed for the corresponding and existing food or drink.

The food and drink of the present invention may be presented or provided in any form usually used in the field of foods and drinks, for instance, products packaged in containers for retort, canned and bottled forms, or in the form of dried products.

The present invention will hereunder be described in more detail with reference to the following Examples, but the present invention is not restricted to these specific Examples at all.

EXAMPLE Preparation of Various Samples:

The following four substances were purchased on the market: γ-L-Glu-L-Abu (Abu: α-aminobutyric acid; available from Bachem Feinchemikalien AG); γ-L-Glu-L-Ala (available from Bachem Feinchemikalien AG); γ-L-Glu-L-Cys (available from Sigma Aldrich Japan Co., Ltd.); and γ-L-Glu-L-Thr (available from KOKUSAN Chemical Co., Ltd).

Synthesis of L-Glu-L-Val:

(Step 1): There were dissolved, in methylene chloride (100 mL), Z-L-Glu-OBzl (N-α-carbobenzoxy-L-glutamic acid α-benzyl ester, 7.619 g, 20.51 mM) and Val-OBzl.HCl (L-valine benzyl ester hydrochloride, 5 g, 20.51 mM) and the resulting solution was maintained at 0° C. There were then added, to the solution, triethylamine (3.2 mL, 22.57 mM), HOBt (1-hydroxybenzo-triazole, 3.053 g, 22.57 mM) and WSC.HCl (1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride, 4.326 g, 22.57 mM) and the resulting mixture was stirred at room temperature overnight. The reaction liquid was then concentrated under reduced pressure and the resulting residue was dissolved in ethyl acetate (220 mL). The solution was fractionated with a 5% citric acid aqueous solution (100 mL) and the aqueous phase thus obtained was further extracted with ethyl acetate (60 mL). The organic phases were combined and then washed in order with a saturated common salt solution (80 mL), a 5% aqueous solution of sodium hydrogen carbonate (80 mL) and a saturated common salt solution (80 mL). The organic phase thus obtained was dried over anhydrous magnesium sulfate, the latter was then removed through filtration and the filtrate obtained was concentrated under reduced pressure. The residue was washed with ethyl acetate/n-hexane (1:1) mixture while maintaining the former in a slurry state and then it was filtered to give Z-L-Glu-L-Val-OBzl (10.0273 g). Moreover, the crystals precipitated from the ethyl acetate/n-hexane fraction by the addition of n-hexane were collected and then recrystallized from ethyl acetate/n-hexane to thus recover Z-L-Glu-L-Val-OBzl (1.0399 g).

Yield: 94.25%.

(Step 2) To ethanol (160 mL), there was added Z-L-Glu-L-Val-OBzl (11.71 g, 20.86 mM), subsequently there were added, to the mixture, a 10% palladium on carbon (2.3 g) and then water (10 mL) and the resulting reaction system was stirred at room temperature overnight in a hydrogen gas atmosphere. Water (100 mL) was added to the system in small portions during the reaction. The palladium on carbon was removed through filtration, the resulting filtrate was concentrated under reduced pressure, the residue thus obtained was recrystallized from a small amount of water and ethanol to thus give γ-L-Glu-L-Val (5.0 g).

Yield: 97.23%.

The characteristic properties of the resulting product are as follows:

ESI-MS: m/z 247.2 (M+H)⁺

¹H-NMR(400 MHz, D₂O): δ (ppm): 0.86 (3H, d, J=6.8 Hz), 0.88 (3H, d, J=6.8 Hz), 2.04-2.13 (3H, m), 2.42-2.46 (2H, m), 3.74 (1H, t, J=6.3 Hz), 4.13 (1H, d, J=5.8 Hz).

Preparation of γ-L-Glu-L-Ser:

According to the same procedures used in the foregoing preparation of γ-L-Glu-L-Val, γ-L-Glu-L-Ser was synthesized while using Z-L-Glu-OBzl and L-Ser-OBzl as starting materials. The characteristic properties of the resulting product are as follows:

ESI-MS: m/z 235.1 (M+H)⁺

¹H-NMR (400 MHz, D₂O): δ (ppm): 1.98-2.09 (2H, m), 2.40 (2H, t, J=8.0 Hz), 3.71-3.81 (3H, m), 4.33 (1H, t, J=8.0 Hz).

Preparation of γ-L-Glu-L-t-Leu:

According to the same procedures used in the foregoing preparation of γ-L-Glu-L-Val, γ-L-Glu-L-t-Leu was synthesized while using Z-L-Glu-OBzl and L-t-Leu-OBzl as starting materials. The characteristic properties of the resulting product are as follows:

ESI-MS: m/z 261.3 (M+H)⁺

Preparation of γ-L-Glu-Aib:

According to the same procedures used in the foregoing preparation of γ-L-Glu-L-Val, γ-L-Glu-Aib was synthesized while using Z-L-Glu-OBzl and Aib-Ot-Bu as starting materials. The characteristic properties of the resulting product are as follows:

ESI-MS: m/z 233.3 (M+H)⁺

¹H-NMR (400 MHz, D₂O): δ (ppm): 1.36 (6H, s), 2.00-2.06 (2H, m), 2.30-2.34 (2H, m), 3.69 (1H, t, J=6.2 Hz).

Test Example 1 Preparation of CaSR-Expression Plasmid

A CaSR-expression plasmid was prepared according to the following procedures:

There were synthesized synthetic oligo DNA used for the PCR procedures (i.e., forward primer (Sequence No. 3: ACTAATACGACTCACTATAGGGACCATGGCATTTTATAGCTGCTGCTGG) and reverse primer (Sequence No. 4: TTATGAATTCACTACGTTTTCTGTAACAG) on the basis of the DNA sequence registered at NCBI (CaSR (calcium receptor): NM_(—)000388, Sequence Nos. 1 and 2).

The PCR procedures were carried out under the conditions specified below using cDNA (available from Clontech Company) derived from human kidney as a material, while using the foregoing primers and Pfu Ultra DNA Polymerase (available from Stratagene Company): The reaction system was processed at 94° C. for 3 minutes and then at 94° C. for 30 seconds, at 55° C. for 30 seconds and at 72° C. for 2 minutes, wherein these steps were repeated over 35 times and the system was finally reacted at 72° C. for 7 minutes. The reaction system was then subjected to electrophoresis treatment through agarose as a support, the agarose was stained with a DNA-staining agent and then it was irradiated with UV light rays to detect whether the cDNA was surely amplified by the PCR procedures or not. At the same time, the electrophoresis pattern was compared with the DNA marker whose electrophoretic size had been known to thus confirm the chain lengths of the PCR products.

Plasmid vector pBR322 was cleaved with a restriction enzyme EcoRV (available from Takara Co., Ltd) and the gene fragment amplified by the PCR procedures was ligated with the plasmid vector at the cleaved site, using Ligation Kit (available from Promega Company). The cells of Escherichia coli DH5 α strain were transformed with this reaction solution, followed by the selection of the transformants containing the plasmid in which the PCR-amplified product had been cloned and further the PCR-amplified product was confirmed by the DNA-base sequence analysis.

This recombinant plasmid was used for the establishment of a human CaSR-Expression Plasmid hCaSR/pcDNA3.1.

Test Example 2 Evaluation of CaSR Agonist Activity

293E Cells (EBNAl-expression HEK293 cells, ATCC No. CRL-10852) were cultivated in DMEN/Ham's-F12 (3.15/mL glucose-containing Dulbecco's modified Eagle medium, available from Nakaraitesk Company) supplemented with 10% fetal calf serum, in the presence of 200 μg/mL of G418 (available from Genetisin). The cultured cells were inoculated in F25 flask at a density of 3×10⁶ cells/10 mL, the flask was allowed to stand over 24 hours in a CO₂ incubator (5% CO₂, 37° C.), and then the human CaSR-expression plasmid hCaSR/pcDNA3.1 was transformed or transfected with a reagent for transfection Fugene6 (available from Roche Company). The transfected plasmid was maintained in a CO₂ incubator over 6 to 7 hours, then the cells were recovered using a 10% fetal calf serum-containing DMEM/Ham's-F12 and the cells were inoculated in each well of a poly-D-lysine coat 96-well plate (BD-Biocoat) at a density of 70,000 cells/well.

The 96-well plate was allowed to stand over 24 hours in a CO₂ incubator, then the culture medium was removed from each well of the 96-well plate in which the cells were inoculated, followed by the addition, to each well, of a Ca²⁺ fluorescent indicator Calcium 4 Assay Kit (available from Molecular Devices Company) dissolved in Assay Buffer (containing 146 mM of NaCl, 5 mM of KCl, 1 mM of MgSO₄, 1 mg/mL of glucose, 20 mM of HEPES (pH 7.2) and 0.75 to 1.25 mM of CaCl₂) in an amount of 200 μl/well, and subsequently allowing the 96-well plate to stand at 37° C. for one hour and then at room temperature for 10 minutes so that the indicator was incorporated into the cells.

To each well of the 96-well plate, there was added each test compound dissolved in a 0.1% BSA-containing Assay Buffer in an amount of 50 μl/well and then any change of the intensity of fluorescence was monitored over 3 minutes using FLEX Station (available from Molecular Devices Company).

(Method for the Determination of EC₅₀):

The difference (RFU (Max-Min)) between the maximum and minimum fluorescent intensities observed for each well before and after the addition of each specific test compound was determined by the automatic calculation using FLEX Station. The activity rate was calculated while the RFU (Max-Min) value observed when adding the compound at the maximum concentration was defined to be 100% and the RFU (Max-Min) value observed when using the 0.1% BSA-containing Assay Buffer free of any test compound was defined to be 0%, followed by subjecting the resulting data to the curve-fitting procedures using the spreadsheet software Xfit or Graph-Pad-Prism to thus determine the EC₅₀ which was the concentration of the compound at the activity rate of 50%. The results thus obtained are summarized in the following Table 1.

TABLE 1 Compound EC₅₀, μM γ-Glu-Abu 0.21 γ-Glu-Ala 1.24 γ-Glu-Val 1.03 γ-Glu-tLeu 3.06 γ-Glu-Cys 0.16 γ-Glu-Ser 11 γ-Glu-Thr 6.97 γ-Glu-Aib 15.4

When comparing with other dipeptides, γ-Glu-Abu was found to have a strong CaSR agonist activity comparable to that observed for γ-Glu-Cys. It has been known that a low molecular weight peptide possessing a CaSR agonist activity is useful as a kokumi-imparting agent (see Patent Document 1 specified above) and accordingly, it is suggested that γ-Glu-Abu would be able to serve as a particularly excellent kokumi-imparting agent.

Example 1 Evaluation of Kokumi-Imparting Activity

In this example, γ-Glu-Abu was inspected for the intensity of its kokumi-imparting activity according to a quantitative sensory evaluation test.

This quantitative sensory evaluation test was carried out according to the following procedures: The intensity of the kokumi-imparting activity observed for each test compound was determined as a value observed when blending 0.001 to 0.5 g/dL of the corresponding test compound to the distilled water containing sodium glutamate (0.05 g/dL), inosine monophosphate (0.05 g/dL), and sodium chloride (0.5 g/dL). In this connection, when a sample showed an acidic nature upon the dissolution of the test compound as compared with the test compound-free control, the pH value of the sample was adjusted, using NaOH, to a level of the pH value (observed for the control)±0.2 prior to the practical use of the sample in the evaluation. The evaluation criteria are assumed to be as follows: control: 0 point; strong: 3 points; very strong: 5 points, while the test was carried out using a panel of n (the number of panelists)=4. Moreover, to make more clear the criteria, the initial taste and the middle/after taste of γ-Glu-Val-Gly at a concentration of 0.001 g/dL were set at 3.0 points, respectively. In this respect, the term “middle/after taste” means the taste detected during the combined period of time extending from the middle taste-sensing period and the after taste-sensing period. The scoring or rating was carried out using the method of line scale and more specifically, it was carried out by writing each corresponding score on a straight line on which points corresponding to −5˜0˜5 had been indicated. The panelists used in this test were defined to be persons who had been engaged in the development of seasonings for foods over not less than one year of the cumulative time period and who could judge that the difference in the titer between γ-Glu-Cys-Gly and γ-Glu-Val-Gly added to a solution having umami/salty taste is about 10 times (while confirming the ability of these persons at regular intervals). The kokumi-imparting agent of the present invention wisely showed the kokumi-imparting activity over the foregoing range of concentration thereof added. The results thus observed for typical concentrations thereof are summarized in the following Table 2.

In addition, γ-Glu-Ala was likewise inspected for its kokumi-imparting effect according to the same procedures used above and the results are also listed in Table 2. The both of these kokumi-imparting agents are initial taste type ones which show high scores for the initial taste, but γ-Glu-Abu was found to be a dipeptide possessing an extremely high titer among others.

TABLE 2 Strength of Kokumi Impartment Middle/ Conc. Initial After Comp. (g/dL) Taste Taste Sensory Evaluation Profile γ-Glu- 0.005 3.8 3.2 Thickness was enhanced from the Abu initial taste stage (giving an impression harmonized with the entire taste) γ-Glu- 0.2 4.5 4.3 Principally, the sour and sweet Ala tastes are enhanced starting from the initial taste stage.

Alternatively, γ-Glu-Cys and other dipeptides were also inspected for the intensity of the kokumi-imparting activity according to the same quantitative sensory evaluation tests as that used above. The results thus obtained are summarized in the following Table 3.

TABLE 3 Strength of Kokumi Impartment Middle/ Conc. Initial After Comp. (g/dL) Taste Taste Sensory Evaluation Profile γ-Glu- 0.01 3.1 3.1 This mainly shows middle and after Cys tastes and emits a slight sulfurous odor. γ-Glu- 0.2 3.6 3.0 This shows a strong initial taste, but Ser emits some foreign tastes. γ-Glu- 0.01 3.1 2.4 This shows a quite weak after taste. Val

Thus, it was found that γ-Glu-Abu possesses an excellent kokumi-imparting activity and that it is also excellent in the rising of the initial taste with respect to the taste-developing or seasoning pattern. This excellent rising of the initial taste observed for γ-Glu-Abu is one of extremely advantageous points thereof as compared with that observed for γ-Glu-Cys. Moreover, γ-Glu-Abu is also excellent in its stability and this is also an advantageous point as compared with γ-Glu-Cys. In addition, γ-Glu-Abu has a short chain length since it comprises only two amino acid residues. Accordingly, it can relatively easily be prepared at a low cost as compared with the preparation of any tripeptide comprising 3 amino acid residues and accordingly, the agent of the present invention is likewise quite advantageous from the industrial standpoint.

Example 2 Determination of Intensity of Kokumi-Imparting Activity

The intensity of γ-Glu-Abu was examined using a testing method for the determination of Point of Subjective Equality (PSE) according to the limit-determining technique (“Statistical Sensory Examination techniques”, written by SATO Shin, published by Japan Federation of Science and Technology).

In this Example, the sensory evaluation was carried out as follows: There was used, as the solution for the sensory evaluation, distilled water containing sodium glutamate (0.05 g/dL), inosine monophosphate (0.05 g/dL) and sodium chloride (0.5 g/dL). As an existing dipeptide possessing a kokumi-imparting effect, there was used γ-Glu-Val. The same level of such an effect can also be observed for γ-Glu-Cys and γ-Glu-Val, but they do not show any particularly intensive initial taste and show the quality of taste different from that of γ-Glu-Abu. γ-Glu-Ala shows the intensity of the kokumi-imparting effect weaker than that of γ-Glu-Val, has a strong sour taste and it is hard to handle since it requires the control of the pH value thereof. Similarly, γ-Glu-Ser shows the intensity of the kokumi-imparting effect weaker than that of γ-Glu-Val, it likewise emits foreign tastes and accordingly, it is hard to handle the same.

To determine the concentration of γ-Glu-Val showing the taste-developing or seasoning effect whose intensity is identical to that of the foregoing solution used for the sensory evaluation test, to which 0.005 g/dL of γ-Glu-Abu was added, there were prepared solutions of γ-Glu-Val whose concentration was varied on a 50% logarithmic scale while using, as standard, the solution used for the sensory evaluation test, to which 0.01 g/dL of γ-Glu-Val was added. The concentration of γ-Glu-Val was changed at 7 stages within the range of from 0.0030 to 0.0337 g/dL. When a sample showed an acidic nature after each test compound was dissolved in the solution for the sensory test, as compared with the pH value of the control free of any test compound, the pH value of the sample was adjusted, using NaOH, to a level of the pH value (observed for the control)±0.2, prior to the practical use of the sample in the evaluation. There were presented to eighteen panelists, these solutions in the ascending order of the γ-Glu-Val concentration and the evaluation tests were continued till each panelist judged that the test solution having a specific concentration showed the kokumi-imparting effect stronger than that observed for the solution containing 0.005 g/dL of γ-Glu-Abu. After putting a certain pause, there were now presented, to the same eighteen panelists, the foregoing solutions in the descending order of the γ-Glu-Val concentration and the evaluation tests were continued till each panelist judged that the test solution having a specific concentration showed the kokumi-imparting effect weaker than that observed for the solution containing 0.005 g/dL of γ-Glu-Abu.

In this sensory evaluation tests, persons who had sufficiently been experienced in the development of food products were used as the panelists. The results thus obtained in these evaluation tests are summarized in the following Table 4.

TABLE 4 Number of Panelists used for Each γ-Glu-Val Concentration Examined: No. of Panelists No. of Panelists No. of Panelists Change who judged who judged that the who judged in that the effect of diff. in the effect that the effect of Stimn. γ-Glu-Val is higher between γ-Glu-Val γ-Glu-Val is weaker Conc. than that observed and of γ-Glu-Abu than that observed of γ- for γ-Glu-Abu (0.0050 g/dL) for γ-Glu-Abu Glu-Val (0.0050 g/dL) is uncertain (0.0050 g/dL) (g/dL) (No. of panelists) (No. of panelists) (No. of panelists) 0.0030 0 0 36 0.0044 1 0 35 0.0067 3 13 20 0.0100 11 13 12 0.0150 25 6 5 0.0225 28 7 1 0.0337 36 0 0

TABLE 5 Lower threshold and upper threshold at which each panelist judged that the samples compared to one another had concentrations identical to each other Method of Lower Threshold Upper Threshold Panelist No. Presentation* (ppm) (ppm) 1 ↑ 55.5 55.5 2 ↑ 83.5 83.5 3 ↑ 55.5 125.0 4 ↑ 55.5 125.0 5 ↑ 55.5 125.0 6 ↑ 125.0 187.5 7 ↑ 37.0 37.0 8 ↑ 55.5 125.0 9 ↑ 55.5 125.0 10 ↑ 125.0 281.0 11 ↑ 55.5 55.5 12 ↑ 55.5 83.5 13 ↑ 83.5 125.0 14 ↑ 83.5 83.5 15 ↑ 125.0 125.0 16 ↑ 187.5 281.0 17 ↑ 55.5 281.0 18 ↑ 83.5 83.5 19 ↓ 125.0 125.0 20 ↓ 83.5 125.0 21 ↓ 187.5 281.0 22 ↓ 83.5 187.5 23 ↓ 83.5 83.5 24 ↓ 55.5 83.5 25 ↓ 83.5 125.0 26 ↓ 55.5 281.0 27 ↓ 55.5 125.0 28 ↓ 187.5 281.0 29 ↓ 187.5 187.5 30 ↓ 55.5 125.0 31 ↓ 125.0 125.0 32 ↓ 83.5 125.0 33 ↓ 56.0 83.5 34 ↓ 281.0 281.0 35 ↓ 55.5 83.5 36 ↓ 125.0 281.0 Confidence — 94.5 149.3 Region (average) PSE 121.9 *Regarding the method of presentation, ↑ means the ascending order of the concentration, and ↓ means the descending order of the concentration.

1) The cases, in which the lower and upper threshold values are identical to one another, correspond to the cases in which it was judged that the difference between the judgments of “stronger” and “weaker” was not determinable or in which any concentration of γ-Glu-Val was not clearly specified. For instance, the panelist No. 1 judged that the intended effect of γ-Glu-Val was weaker than that observed for γ-Glu-Abu at the γ-Glu-Val concentration of 44 ppm (0.0044 g/dL), while he judged that the effect was stronger than that observed for γ-Glu-Abu at the γ-Glu-Val concentration of 67 ppm (0.0067 g/dL) and accordingly, the lower threshold value (55.5 ppm) and the upper threshold value (55.5 ppm) are identical to one another.

2) The “confidence region (or value)” is herein defined to be the average of the lower threshold value and the upper threshold value.

The point of subjective equality (PSE) of γ-Glu-Val relative to the 50 ppm (0.0050 g/dL) of γ-Glu-Abu is defined to be as follows: (Sum of the confidence value of the lower threshold value and that of the upper threshold value)÷2.

The concentration of γ-Glu-Val (PSE) showing the desired effect whose intensity is identical to that observed for 0.0050 g/dL of γ-Glu-Abu would be assumed to be about 0.0100 g/dL while taking the number of panelists shown in Table 4 into account. If PSE is calculated on the basis of the upper and lower threshold values of γ-Glu-Val, at which each individual panelist judges that the effects observed for these two dipeptides are equivalent to each other, it is found to be 0.0122 g/dL. In this connection, the intensity of the desired kokumi-imparting effect of γ-Glu-Abu was found to be about 2.4 times that observed for γ-Glu-Val and accordingly, it could be so concluded that the former is a dipeptide having extremely high intensity of the effect. Thus, γ-Glu-Abu can be said to be a valuable dipeptide which can easily be prepared as compared with the conventionally known substances and which can show the kokumi even at the initial taste stage when applied to a wide variety of foods.

Example 3 Evaluation of Effect of γ-Glu-Abu on Enhancement of Salty Taste

In this Example, γ-Glu-Abu was inspected for its salty taste-enhancing effect according to the quantitative sensory evaluation tests.

The sensory evaluation tests were carried out according to the following method: A test compound in an amount, which was considered to be optimum, was added to distilled water containing sodium chloride (0.5 g/dL) and the intensity of the salty taste-enhancing effect thereof was determined. When a sample showed an acidic nature after each test compound was dissolved in the solution for the sensory test, as compared with the pH value of the control free of any test compound, the pH value of the sample was adjusted, using NaOH, to a level of the pH value (observed for the control)±0.2, prior to the practical use of the sample in the evaluation.

Regarding the score of the sensory evaluation, the effect was evaluated within the range extending from -5 to 0 to 5, on the assumption that the control free of any compound or the aqueous solution of sodium chloride having a concentration of 0.5 g/dL was evaluated to have a score of 0 and that the aqueous solution of sodium chloride having a concentration of 0.75 g/dL was evaluated to have a score of 5, while the number of panelists (n) constituting each panel was set at 5. The term “initial taste” herein means the taste impression detected by each panelist during the term extending from the time of eating the sample to 2 seconds thereafter, while the term “middle/after taste” means that detected by each panelist during the term from 2 seconds on, after eating the same, or during the term combining the middle taste-sensing period and the after taste-sensing period. The scoring or rating was carried out using the linear standard technique and more specifically, it was carried out by writing each corresponding score on a straight line on which points corresponding to −5˜0˜5 had been indicated. The panelists used in this test were defined to be persons who had been engaged in the development of seasonings for foods over not less than one year of the cumulative time period and who could judge that the difference in the titer between γ-Glu-Cys-Gly and γ-Glu-Val-Gly is about 10 times (while confirming the ability of these persons at regular intervals). The results thus obtained are summarized in the following Table 6.

TABLE 6 Strength of Salty Taste Impartment Middle/ Conc. Initial After Comp. (g/dL) Taste Taste Sensory Evaluation Profile γ-Glu- 0.004 1.6 1.5 The salty taste was enhanced even Abu from the initial taste period and sharpness of salty taste was also imparted. γ-Glu- 0.002 0.8 1.8 The sample loses the characteristics Val-Gly as an initial taste type one.

In this Example, γ-Glu-Val-Gly as a tripeptide having a high titer with respect to the kokumi-imparting ability was compared with γ-Glu-Abu as a dipeptide according to the present invention. As a result, it would be concluded that γ-Glu-Val-Gly shows an intensity of taste-imparting activity higher than that observed for γ-Glu-Abu, while taking into consideration the concentration used for the evaluation and the resulting scores. As also shown in the sensory evaluation profile, however, the balance of the salty taste is considerably lowered in case of γ-Glu-Val-Gly. On the other hand, γ-Glu-Abu can enhance the salty taste in a considerably well-balanced manner and accordingly, γ-Glu-Abu may particularly be suitable as a salty taste-enhancing peptide.

Example 4 Evaluation of Effect of Organic Acid Used in Combination

In this Example, the effect of the use of an organic acid in combination on the salty taste-enhancing effect of γ-Glu-Abu was investigated according to the quantitative sensory evaluation test.

The sensory evaluation tests were carried out according to the following procedures. Low salt “Whole Chicken Stock” commercially available from Ajinomoto Co., Ltd. was dissolved in hot water so that the resulting solution had a common salt concentration of 0.48 g/dL, then an appropriate amount of each test compound was dissolved in the solution and the intensity of the salty taste was determined. The pH value of the sample solution obtained after dissolving each test compound was not different from that of the control free of any added compound and accordingly, any control of the pH value was not required. In the sensory evaluation, there was not recognized any influence of, for instance, the sour taste. Regarding the score of the sensory evaluation, to make more clear the criteria for the evaluation, the evaluation criteria for the salty taste are assumed to be as follows: the control: 3 points; the salty taste observed for a soup prepared by increasing the salt concentration to 1.25 times that of the control: 4 points; and the salty taste observed for a soup prepared by increasing the salt concentration to 1.5 times that of the control: 5 points, while the test was carried out using a panel of n (the number of panelists)=6. The scoring or rating was carried out using the linear standard technique and more specifically, it was carried out by writing each corresponding score on a straight line on which points corresponding to 1˜3˜5 had been specified. The panelists used in this test were defined to be persons who had been engaged in the development of seasonings for foods over not less than one year of the cumulative time period and who could judge that the difference in the titer between γ-Glu-Cys-Gly and γ-Glu-Val-Gly is about 10 times (while confirming the ability of these persons at regular intervals). The results thus obtained are summarized in the following Table 7.

TABLE 7 Str. of Salty Conc. Taste Sensory Evaluation Compound (g/dL) (score) Profile γ-Glu-Abu 0.0040 3.56 The salty taste as the initial taste was enhanced. Combined γ-Glu-Abu 0.0040 3.92 The salty taste impression Use 1 Lactic acid 0.0300 as the initial taste was enhanced and the overall thickness of the soup was improved. Combined γ-Glu-Abu 0.0040 3.76 The salty taste observed Use 2 Malic acid 0.0300 during the term extending from the initial taste stage to the after taste stage was enhanced and the overall thickness of the soup was improved.

It was thus found that lactic acid and malic acid as organic acids were quite congenial to γ-Glu-Abu and that the salty taste-enhancing effect of γ-Glu-Abu was further improved by the use of lactic acid and malic acid, as organic acids, in combination with the former.

In other words, such an effect of γ-Glu-Abu that the salty taste is enhanced in a well-balanced manner can further be improved by the use of an organic acid in combination with the dipeptide. Accordingly, γ-Glu-Abu can be prepared from cheap and currently and widely used materials and is a compound which can further improve the taste-imparting effects of the conventionally known substances.

While the invention has been described in detail with reference to preferred embodiments thereof, it will be apparent to one skilled in the art that various changes can be made, and equivalents employed, without departing from the scope of the invention. Each of the aforementioned documents is incorporated by reference herein in their entireties. 

1. A kokumi-imparting agent comprising γ-Glu-Abu.
 2. A complex kokumi-imparting agent comprising, in combination, (a) γ-Glu-Abu; and (b) one or at least two amino acids or peptides selected from the group consisting of γ-Glu-X-Gly wherein X represents an amino acid or an amino acid derivative, γ-Glu-Val-Y wherein Y represents an amino acid or an amino acid derivative, γ-Glu-Ala, γ-Glu-Gly, γ-Glu-Cys, γ-Glu-Met, γ-Glu-Thr, γ-Glu-Val, γ-Glu-Orn, Asp-Gly, Cys-Gly, Cys-Met, Glu-Cys, Gly-Cys, Leu-Asp, D-Cys, γ-Glu-Met (O), γ-Glu-γ-Glu-Val, γ-Glu-Val-NH₂, γ-Glu-Val-ol, γ-Glu-Ser, γ-Glu-Tau, γ-Glu-Cys (S-Me) (O), γ-Glu-Leu, γ-Glu-Ile, γ-Glu-t-Leu and γ-Glu-Cys (S—Me).
 3. A seasoning composition comprising not less than 1,000 ppm by mass of γ-Glu-Abu.
 4. The seasoning composition as set forth in claim 3, wherein it comprises not less than 2,500 ppm by mass of γ-Glu-Abu.
 5. A method for preparing an intermediate used for the preparation of a food or drink comprising the steps of: adding an ingredient for foods or drinks, which contains not less than 1000 ppm by mass of γ-Glu-Abu, to the other ingredient for foods or drinks; and further cooking, at need, the resulting mixture of the ingredients for foods or drinks.
 6. The method for preparing an intermediate used for the preparation of a food or drink as set forth in claim 5, wherein the step of adding an ingredient for foods or drinks containing γ-Glu-Abu to the other ingredient for foods or drinks further comprises the step of controlling the concentration of γ-Glu-Abu in the intermediate used for the preparation of a food or drink to a level ranging from 400 to 500,000 ppm by mass.
 7. The method for preparing an intermediate used for the preparation of a food or drink as set forth in claim 6, wherein it further comprises the step of adding the intermediate used for the preparation of a food or drink to the other ingredient for foods or drinks to thus control the concentration of γ-Glu-Abu to a level ranging from 20 to 200 ppm by mass.
 8. The method for preparing an intermediate used for the preparation of a food or drink as set forth in claim 5, wherein the step of adding an ingredient for foods or drinks containing γ-Glu-Abu to the other ingredient for foods or drinks further comprises the step of controlling the concentration of γ-Glu-Abu in the foods or drinks to a level ranging from 20 to 200 ppm by mass.
 9. The method for preparing a food or drink as set forth in claim 5, wherein the food or drink is a low salt food or drink.
 10. The method as set forth in claim 9, wherein it further comprises the step of adding, to an ingredient for a food or drink, at least one organic acid or salt thereof selected from the group consisting of lactic acid, citric acid, malic acid and succinic acid and salts thereof, in a concentration thereof in the resulting food or drink ranging from 0.005 to 0.1% by mass.
 11. A food, a drink or an intermediate used for preparing a food or drink which is obtainable by the method as set forth in claim
 5. 12. A food, a drink or an intermediate used for preparing a food or drink comprising, the total mass of the food, the drink or the intermediate for foods or drinks, 20 to 200 ppm by mass of γ-Glu-Abu; 0.005 to 0.1% by mass of at least one organic acid or a salt thereof selected from the group consisting of lactic acid, citric acid, malic acid and succinic acid; and 0.01 to 0.5% by mass of common salt, as well as a carrier acceptable for foods and drinks and/or one or at least two seasoning ingredients.
 13. A method for enhancing the taste of a food or a drink comprising the step of incorporating, into a food or a drink, a composition which comprises not less than 400 ppm by mass of γ-Glu-Abu.
 14. The method as set forth in claim 13, wherein the taste-enhancement is imparting kokumi to the food or drink. 